Hexavalent chromium removal in a tannery industry wastewater using rice husk silica

7/21/2019 Hexavalent chromium removal in a tannery industry wastewater using rice husk silica

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Global J. Environ. Sci. Manage., 1 (1): 27-40, Winter 2015

Received 1 October 2014; revised 3 November 2014; accepted 28 November 2014; available online 1 December 2014

ABSTRACT: Present study dealt the removal of Cr(VI) in a tannery industry wastewater using rice husk silica powder

as an adsorbent.The experimental investigations have been carried out by using rice husk silica powder for different

adsorption dosage, different contact time and different pH against the initial Cr(VI) concentration of 292 mg/L. The

maximum percentage removal of Cr(VI) in a tannery industrial wastewater (88.3 %) was found at an optimum adsorbent

dosage of 15 g, contact time of 150 min., and pH of 4. Further, the experimental data on removal of Cr(VI) from tanneryindustry wastewater was validated with the Cr(VI) aqueous solution of same initial concentration of tannery industry

wastewater against the optimum process parameters. The results of the validation experiment showed that the experiments

conducted for the removal of Cr(VI) in a tannery industry wastewater may be reproducing capability for analyzing

various parameters along with Cr(VI) based water and industry wastewater. The experimental data were fitted to

Langmuir and Freundlich isotherm models. Isotherm models result indicated that the equilibrium data fitted well with

the Langmuir isotherm than Freundlich isotherm, because of higher correlation created between dependent and independent

variables. Thus, the adsorption method using rice husk silica powder was used effectively for removing Cr(VI) in the

tannery industrial wastewater, seems to be an economical and worthwhile alternative over other conventional methods,

because of their abundant source, low price, multi-purposes and antimicrobial properties.

Keywords:Adsorption, Isotherm models, Magnetic stirrer, Tannery industry wastewater, UV/VIS spectrophotometer


ISSN 2383 - 3572

*Corresponding Author Email: [email protected]

Tel.: +91 44 26580451; Fax: +91 44 26580451

Hexavalent chromium removal in a tannery industry wastewater using

rice husk silica

*D. Sivakumar

Department of Civil Engineering, Vel Tech High Tech Dr.Rangarajan Dr.Sakunthala Engineering College,

Avadi, Chennai, Tamil Nadu, India

INTRODUCTION

Development of rapidly increasing industry and

population growth, utilization of water for various

purposes increases tremendously, as a result, sources

of water are polluted by discharging wastewater from

both industry and domestic sectors (Sivakumar

Durairaj, 2013c). When compared to water pollution

caused by domestic sector, pollution caused by

industry sector contributes more (Olayinkaet al., 2007).

Heavy metal contamination is a serious environmental

issue of global concern, particularly in developing

countries (Kleckerova and Doeekalova, 2014; Akoto

et al., 2014).

In the developing countries, heavy metals

containing effluent are continuously released from

thousands of small and large-scale industries such as

metallurgy, battery manufacturing, mine drainage,

chemical manufacturing, leather tanning and

electroplating industries etc. (Oladoja et al., 2013;

Rameshraja and Suresh, 2011) directly or indirectly into

the natural water resources, mostly without proper

treatment, posing a major threat to the environment.

Today, the heavy metals like Cu, Zn, Ni, Pb, Cd, and

Cr into various sources of drinking water pose a great

threat to public health. Among these heavy metals,

pollution by chromium is of major concern as the metal

is used in electroplating, leather tanning, metal

finishing, and chromate preparation. Chromium is one

of the heavy metals used by modern industries like

plastic, pigment, wood preservative, electroplating,

leather tanning, cement, mining, dyeing and fertilizer

(Oladoja et al., 2013). Among them, chrome tanning

industry contributes more chromium pollution in water

and land environment (Sudipta et al., 2012). Chromium

occurs in aqueous systems as trivalent and hexavalent

forms. However, the latter form is of particular concern

due to its carcinogenic and mutagenic effects (Oladoja
mailto:[email protected]:[email protected]:[email protected]


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28

et al., 2013). Human is facing the problems like gastric

system, epigastric pain, nausea, vomiting, severe

diarrhea, corrosion of the skin, respiratory tract and lung

carcinoma when consumed the chromium polluted water.

In addition to chromium, wastewater generated fromthese industries contains much higher concentrations

of properties like colour, total dissolved solids,

suspended solids, phenols, chlorides, ammonia, and

other heavy metals (Sivakumar and Shankar, 2012a,

2012b). The discharged wastewater has generally

contaminated the surface water and groundwater, results

increased water pollution also soil is contaminated due

to discharge wastewater (Sivakumar, 2011). The

maximum permissible limit of chromium content in

drinking water is 0.05 mg/L (WHO, 1996). Recently,

increasing awareness of water and wastewater pollution

and its far reaching effects has prompted concertedefforts towards pollution abatement.

Removal of Cr(VI) ions from industrial wastewater is

achieved principally by the application of several

conventional processes such as reduction followed by

chemical precipitation (Karale et al., 2007; Sarin and Pant,

2006), absorption (Sivakumar, 2013 a), activated carbon

(Ghosh, 2009), electrochemical processes (Golderet al.,

2011), ion exchange (Rafati et al., 2010; Balan et al.,

2013), biological operations (Sivakumar Durairaj, 2013c),

catalytic oxidation (Kennedy et al., 2004) and membrane

processes (Sarin and Pant, 2006) etc. These methods

require large amounts of chemical substances and energy,

generation of toxic sludge, fouling, high capital andoperational costs, expensive equipment requirement and

efficient monitoring system (Demirbas et al., 2004;

Demiralet al., 2008).

Adsorption is a simple and low cost method used for

removing Cr(VI) from any aqueous solution (Chuah et

al., 2005; Gholami et al., 2006; Sarin and Pant, 2006).

The main advantages of the adsorption method are that

single or multiple ions present in the any aqueous

solution adhered onto porous solid surface and can be

separately and quantitatively determined (Jal et al., 2004;

Oladoja et al., 2013). The other advantages include low

cost, high efficiency of metal removal from dilutesolutions, minimization of chemical, biological sludge,

no additional nutrient requirement and regeneration of

absorbent and possibility of metal recovery (Sivakumar,

2013b). The various adsorbents have been used for

removal of Cr(VI) in aqueous solution and industrial

wastewater like silica gel (Katsumata et al., 2003), river

sand (Sharma and Weng, 2007), manganese-coated

sand (Lee et al., 2010), fly ash (Sharma et al., 2008),

coconut shell (Pino et al., 2006), wheat bran (Nameni

et al., 2008), rice bran (Oliveira et al., 2005), etc.

This study mainly concentrated on removal of Cr(VI)

from tannery industry waster than aqueous solution usingrice husk silica. Rice husk silica is derived from the rice

husk. Rice husk is the by-product of the rice milling

industry. RHA is light in weight and has approximately

15-20 % of paddy weight (Liou and Wu, 2009). Rice husk

ash is produced from the combustion of rice husk. The

colour of RHA varied from white to gray (Muhammad et

al., 2013). Rice husk is commonly used as a low-value

energy resource, burned in the field, and or discarded

into the environment (Chen et al., 2011; Lin et al., 2013).

Rice husk mainly consists of ash and organic matter, which

comprises an organic cellulose, hemi-cellulose, lignin (Liou

and Wu, 2010; Wang et al., 2010) and inorganic silicondioxide (Wang et al., 2010). Further, Farook, et al., 2006

reported that rice husk is composed of 20 % ash, 32.2-38

% cellulose (Mahvi et al., 2004; Chuah et al., 2005), 21.3-

22 % lignin (Mahvi et al., 2004; Chuahet al., 2005), 21.4 %

hemi-cellose (Mahvi et al., 2004; Chuah et al., 2005), 18 %

pentose, and 2 % of other organic components (Adam et

al., 2006). As rice husk is insoluble in water, having good

chemical stability, structural strength due to the high silica

content (Lee et al, 1994).

RHA, produced after the burning of Rice husks (RH)

has high reactivity and pozzolanic property (Tomas,

2013). Rice husk ash is used as supplemental material

for cement and concrete cube manufacturing industries

(Della et al., 2002). It is also used as additives for soil

stabilization, as adsorbent for removal of contaminants

from contaminated water and wastewater. Preparation

of useful products from rice husk eliminates the

disposal problem. Rice husk ash contains nearly 90-96

% of silica (Thankappan et al., 2006), which may be

used as one of the ingredients for making ceramic

(Farooket al., 2006; Liou and Wu, 2009), polymers and

electronic products, it has highly porous and light in

weight, with a very high external surface area (Kumar

et al., 2013). Silica was extracted from rice husk ash

(RHA) and used to produce a corrosion inhibitor forcarbon steel (Denni et al., 2013). Because of easy to

convert organic components into carbonaceous

substances from rice husk (Kennedy et al., 2004; Chen

et al., 2013), a greater attention has been made

nowadays by many researchers. There are several

studies used rice husk derived adsorbent (rice husk,

rice husk carbon, rice husk ash and rice husk silica) for

D. Sivakumar


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removal of Cr (VI) from aqueous solution (Srinivasan

et al., 1988; Della et al., 2002; Bhattacharya et al., 2006;

Singha et al., 2011; Singh and Singh, 2012; Anand et

al., 2014; Apeksha and Mote, 2014).

Thus, this study focused to investigate the effect ofadsorption dosage, contact time and pH against the initial

concentration of Cr(VI) in a tannery industry wastewater

using rice husk silica powder. The experimental results of

Cr(VI) in a tannery industry wastewater using rice husk

silica powder were validated with the Cr(VI) in an aqueous

solution and other parameters in a tannery industry

wastewater. Further, the experimental data were fitted to

Langmuir and Freundlich isotherm models for determining

the suitability of rice husk silica for removing Cr(VI) in a

tannery industry wastewater. All experiments were

conducted in the Environmental Engineering Laboratory,

Department of Civil Engineering, Vel Tech High TechDr.Rangarajan Dr.Sakunthala Engineering College, Avadi,

Chennai, Tamil Nadu, INDIA, during December 2013.

MATERIALS AND METHODS

Study Area

The selected study area of this present study is

Nagalkeni, which is situated in Kanchipuram District,

Tamil Nadu with 12.96 Latitude and 80.14 Longitude

(Fig. 1).The groundwater of Nagalkeni is polluted by

untreated sewage and wastewater from tannery

industry. Furthermore, the porous media (the soil) in

Nagalkeni are also contaminated, when untreated

sewage and wastewater from tannery industry is

discharged on the land. The tannery industry

wastewater contained heavy metals, particularly Cr (VI),which is carcinogenic to human beings when the

concentration of Cr(VI) exceed the tolerance limit of

0.05 mg/L (BIS drinking water quality standard - IS

10500:1991).

Adsorbent Preparation

Rice husk collected from rice mill was mixed together

to form a homogeneous mixture. Then, a homogeneous

mixture of rice husk was thoroughly washed with tap

water to clean dirt and mud. Silica may be obtained

from rice husk through different methods (Nittaya and

Apinon, 2008; Tzong-Horng Liou, 2004; Della et al.,2002). In this paper, the cleaned rice husk was mixed

with 1.0 M HCl in the ratio of 100 g rice husk per 1 litre

acid and heated to the temperature of 100 C for 2 hours.

At the end of 2 hours reaction, the trace of HCl acid

within the treated rice husk was removed by washing

with tap water. Then, it was dried in an oven at 130 C

for 24 hours. During, this period, rice husk ash was

obtained from the rice husk and the colour of rice husk

ash is in black. Further, the rice husk ash was heated to

a temperature of 650 C for 6 hours to obtain silica.

Fig.1: Study area of Nagalkeni

N


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Rice husk silica was produced by a solgel method

(Qu et al., 2010). Oladoja et al., (2013) and Farooket al.,

(2006) obtained the silica from rice husk by thermal

treatment with the temperature of 700 C for 5 hours. In

this study, silica is prepared by physical activation, i.e.,gasification of chars in an oxidizing atmosphere (Swarna

latha et al., 2013) followed by chemical activation, i.e.,

carbonization of carbonaceous materials impregnated

with chemical reagents (Oladoja et al., 2013; Farooket

al., 2006). The obtained silica from the rice husk was

white in colour. Since the heating temperature of 300 C

for 1 h, the ash produced from the rice husk found to be

black in colour (Fig. 2). The colour of the rice husk ash

turned from black to blackish white, gray and white

respectively, for the temperature 400 C (Fig. 3), 500 C

(Fig. 4) and 650 C ( Fig. 5). The colour changes from

blackish white, gray and white was achieved for the

time period of 2, 4 and 6 h respectively. The black

colour of rice husk ash contains carbon content of

64.8 % (300 C for 1 h), the blackish white colour ofrice husk ash contains carbon content of 37.3 % (400

C for 2 h), gray colour of rice husk ash contains

carbon content of 15.9 % (500 C for 4 h), and white

colour of rice husk ash contains carbon content of

0.26 % (650 C for 6 h). The same result was observed

by Della et al., (2002) and Oladoja et al., (2013). The

rice husk silica was further grained to fine particles of

uniform geometrical size of 0.10 mm, which were used

for treating removal of Cr(VI) from tannery industry

wastewater.

Fig. 4: Rice husk ash (500 C for 4 h) Fig. 5: Rice husk silica (650 C for 6 h)

Fig. 2: Rice husk carbon (300 C for 1 h) Fig. 3: Rice husk ash (400 C for 2 h)

Hexavalen t chromiu m removal


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Properties

Physical Properties

Specific surface, m2/g

pH

Moisture content, %

Density, g/cm3

Chemical Properties

SiO2Al

2O

3

CaO

NaO

K2O

Fe2O

3

MgO

Loss on Ignition

Other Impurities

31

The physical and chemical properties of rice husk silica

were presented in Table 1. The specific surface area was

determined by the nitrogen adsorption according to B.E.T.

equation (Della et al., 2002; Nittaya and Apinon, 2008).

The pH was measured using a pH meter (Sivakumar, 2012).The moisture content was determined by the oven dry

weight method and density was determined using

Pycnometer (Punmia, 2005). APHA, (2005) procedures

were followed for the determination of chemical properties

in a tannery industry wastewater.

From Table 1, it may be observed that silica contributes

more fraction than other constituents of the rice husk

ash. Della et al., (2002) reported that the silica presented

in the rice husk ash is about 94.95 %, which was achieved

when the rice husk was calcined at 700 C for 5 h. Nittaya

and Apinon, (2008) produced the silica of 90.3 % from

rice husk, when rick husk being treated by 2.5 N sodiumhydroxide with 700 C for 3 h and 98.14% silica was

achieved with the heat treatment of 700 C for 6 h.

Collection of Wastewater Sample

Totally five wastewater samples were collected

without the presence of bubbles using cleaned air tight

plastic bottles, took to the laboratory and then they

were stored for analyzing Cr(VI) and other basic

parameters. Various physico-chemical parameters such

as pH, total dissolved solids (TDS), total solids (TS),

chemical oxygen demand (COD), biochemical oxygen

demand (BOD), and sulphate (SO4

2-) in a homogenized

wastewater samples were analyzed before and after

treating with rick husk silica by using standard

procedures prescribed in APHA, 2005. The Cr(VI) was

also measured in a homogenized wastewater sample

before and after treating with rice husk silicausing UV/

VIS spectrophotometer (APHA, 2005). In this method,first prepared stock solution by dissolving 141.4 mg of

dried potassium dichromate in distilled water of 100

mL and kept in a volumetric flask and by dissolving

250 mg 1,5 Diphenyl carbazide in 50 mL acetone in a

dark brown coloured bottle to prepare a stock solution.

Prepared a series of reference solutions by pipetting

known quantity of chromium stock solution (0.02, 0.04,

0.06, 0.08, 0.1, 0.12, 0.14, 0.16 mg/L) into 100 mL

volumetric flasks. Adjust pH of the solution to 2.0 0.5

with 0.25 mL phosphoric acid and 0.2 N sulfuric acid,

mix well and dilute with distilled water. In order to

develop colour, added 2.0 mL of Diphenyl carbazide tothe solutions, mix well and allow the solutions to stand

for 10 min. Then the absorbance measurements were

performed at the wavelength of 540 nm using the Perkin

Elmer UV/VIS spectrophotometer. The physico-

chemical characteristics and Cr(VI) in a tannery industry

wastewater are given in Table 2.

Experimental Arrangement

The adsorption capacity ofthe rice husk silica

powder on removal of Cr(VI) in a tannery industry

wastewater was performed in this present study. The

size silica particle used in this study was 0.10 mm. The

experiments were conducted for different adsorbentdosage of 5, 10, 15, 20 g, contact time of 30, 60, 90, 120,

150, 180 min., agitator speed of 250, 500, 750, 1000

rpm, dilution ratio of 0, 1, 2, 3, 4, 5 and pH of 2, 3, 4 5, 6,

7, 8 and 9 (different process parameters). Tannery

industry wastewater was taken in 4 glass beakers of

250 ml capacity and was kept on the magnetic stirrer

Table 1: Physical and chemical properties of rice husk silica

Table 2: Characteristics of tannery industry wastewater

Sl.No.

1

2

3

4

5

6

7

Characteristics

pH

TDS

TS

COD

BOD

Sulphate

Chromium

Values

7. 6

12350 mg/L

16625 mg/L

8256 mg/L

5689 mg/L

852 mg/L

292 mg/L

18 6

6. 0

0. 7

2.20

Values

95.3 %0.3 %

1.3 %

0.45 %

1.4 %

0.5 %

0.8 %

0.3 %

0.15 %


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apparatus for different adsorbent dosage, different

contact time, different agitations speeds, different

concentration dilutions and different pH. The treated

tannery industry wastewater with rice husk silica

against various process parameters was allowed tosettle for 24 h, and then it was filtered. Further, the

reduction in concentrations of Cr(VI) in a tannery

industry wastewater wasanalyzed by a digital UV/VIS

spectrophotometer. The other physico-chemical

parameters also determined by using the standard

procedure stipulated by APHA, 2005. The adsorption

removal percentage of various parameters such as

Cr(VI), pH, TDS, TS, COD, BOD, and SO4

2-in a tannery

industry wastewater by rice husk silica powder was

calculated by using the following formula:

Percentage Removal:

in which Cois the concentration of Cr(VI), pH, TDS,

TS, COD, BOD, and SO4

2- in a tannery industry

wastewater before treatment (time t = 0 min.) with

rice husk silica powder and Ctis the concentration of

Cr(VI), pH, TDS, TS, COD, BOD, and SO4

2- in a

tannery industry wastewater after treatment with rice

husk silica powder (t = t min.). This study mainly

focuses on removal of Cr(VI) in a tannery industry

wastewater rather than other physico-chemical

parameters. But, the other physico-chemical

parameters are used to check the validity of rick husk

silica powder for the removal of Cr(VI) in a tannery

industry wastewater. Thus, the equilibriumexperimental data of Cr(VI) are used to fit the

isotherm models. Using a mass balance, the

concentrations of Cr(VI) at different time adsorbed

by rice husk silica powder was calculated as

in which, qtis the amount of Cr(VI) adsorbed by the

rice husk silica powder at time t, Ci is the initial

concentration of Cr(VI), V is the volume of the

aqueous phase, Mis the weight of rice husk silica

powder.

RESULTS AND DISCUSSION

In the present study, Cr(VI) in a tannery industrial

wastewater was reduced using the method called

adsorption. The selected process parameters of this

adsorption methodare different adsorption dosage,

different contact time and different pH. The results are

presented below.

Effect of adsorption dosage

The Fig. 6 showsthe effect of adsorption dosage in

the removal of Cr(VI) from tannery industry wastewater.

The selected adsorption dosage was 5, 10, 15 and 20 g

for the contact time of 90 min., and pH of 7 against aninitial Cr(VI) concentration of 292 mg/L (0 dilution

ratio). From Fig. 6, it may be observed that the

percentage removal of concentration of Cr(VI) by rice

husk silica powder with the adsorption dosage of 5,

10, 15 and 20 g was found to be 47.4, 56.3 and 64.5 and

60.8 % respectively. From Fig. 7, it may be observed

that till the adsorbent dosage reaches to 15.0 g, the

removal percentage of Cr(VI) in a tannery industry

wastewater increased, beyond which removal

percentage got decreased. The less removal rate of

Cr(VI) in a tannery industry wastewater for the dosage

of 5.0 g, 10.0 g is due to less availability of specificsurface area of rice husk silica. Further, the less removal

rate of Cr(VI) in a tannery industry wastewater for the

dosage of 20.0 g is due to the agglomeration of rice

husk silica, results, which is not exposing the surface

area to adhere the Cr(VI) from tannery industry

wastewater (Sivakumar and Shankar, 2012). Thus,

optimum adsorption dosage for which, maximum

removal of Cr(VI) in tannery industry wastewater

(64.5 %) is found to be15 g (Fig. 6).

Effect of contact time

The Fig. 6 shows the effect of contact timeof removal

of Cr(VI) in a tannery industry wastewater. The selected

contact time was 30, 60, 90, 120, 150, and 180 min. for

anoptimum adsorption dosage of 15 g, and pH of 7

against an initial Cr(VI) concentration of 292 mg/L (0

dilution ratio). From Fig. 7, it may be observed that the


husk silica powder with the contact time of 30, 60, 90,

120, 150, and 180 min. was found to be 34.5, 46.5, 54.6,

62.8, 68.4 and 64.6 % respectively. From Fig. 3, it may

be observed that till the contact time reaches to 150

min., the removal percentage of Cr(VI) in a tannery

industry wastewater increased, beyond which removal

percentage got decreased. The less removal rate ofCr(VI) in a tannery industry wastewater for the contact

time of 30, 60, 90, 120 min. is due to the larger surface

area of rice husk silica was not contacted properly with

the tannery industrywastewater. Further, the less

removal rate of Cr(VI) in a tannery industry wastewater

for the contact time 180 min.is due to presence of

exhausted sites on the surface of rice husk silica, results,

(1)

D. Sivakumar

Percentage Removal:

( ci- c

t) V (2)

qt=

M

( c0- c

t)

c0* 100


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the adsorbent is transported from the exterior to the

interior sites of the adsorbent particles (Sivakumar and

Shankar, 2012). Thus, optimum contact time for which,

maximum removal of Cr(VI) in tannery industry

wastewater (68.4 %) is found to be 150 min. (Fig. 7).

Effect of pH

The Fig. 8 shows the effect of pHon removal of Cr(VI)

in a tannery industry wastewater. The selected pH ranges

was 2, 3, 4, 5, 6, 7, 8, and 9 for an optimum adsorption

dosage of 15 g and optimum contact time of 150 min.

against an initial Cr(VI) concentration of 292 mg/L (0

dilution ratio). From Fig. 8, it may be observed that the


husk silica powder with the pH range of 2, 3, 4, 5, 6, 7, 8

and 9 was found to be 62.3, 79.6, 88.3, 84.6, 80.3, 76.4,

73.1 and 69.2 % respectively. From the Fig. 4, it may be

observed that at low pH, hydrogen ions in the tanneryindustry wastewater were not allowing the Cr(VI) ion to

adhere with the binding sites of rice husk silica. At high

pH, a tannery industry wastewater becomes basic and

rice husk silica released more hydroxyl groups making

the tannery industry wastewater more basic (Sivakumar,

2013); as a result, Cr(VI) ion was not adhering into the

binding sites of adsorbents. Thus, an optimum pH value,

for which, maximum removal of Cr(VI) in a tannery

industry wastewater (88.3 %) is found to be 4 (Fig. 8).

Validation of Experiment

Validation of experiment is required to verify the

finding of similarities against the observed values of

an experimental investigation. This validation

experiment is used to check the degree of similarity

between the adsorption experiments conducted at an

optimum adsorbent dosage of 15 g, optimum contact

time of 150 min. and optimum pH of 4 against an initial

Cr(VI) concentration of 292 mg/L in a tannery industry

wastewater using rice husk silica powder with the new

experiments (separate experiments) conducted against

the same optimum values of adsorbent dosage, contact

time, pH against an initial Cr(VI) concentration of 292

mg/L in an aqueous solution using rice husk silica

powder. The maximum removal of Cr(VI) in a tannery

industry wastewater and an aqueous solution

usingrice husk silica powder at optimum values of

selected parameters is shown in Fig. 9. The results ofvalidation experiments showed that the maximum

removal percentage of Cr(VI) in an aqueous solution

using rice husk silica powder at the optimum conditions

is greater than (93.5 %) the results of Cr(VI) removal in

a tannery industry wastewater (88.3 %) by rice husk

silica powder. From Fig. 5, it may be noted that the

high values observed in a Cr(VI) aqueous solution than

in a tannery industry wastewater is due to there are no

competitive ions present in aqueous solution than in a

Fig. 6: Effect of adsorption dosage of removal of Cr(VI) in a tannery industry wastewater

0.0 5.0 10.0 15.0 20.0 25.0

Adsorption Dosage (g)

0. 0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

PercentageRemoval


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tannery industry wastewater, where the competitive

ions like chloride, sulphate, acids, alkaline and other

trace metals are presented.

Further, the obtained maximum removal percentage

of Cr(VI) in a tannery industry wastewater using rice

husk silica powder with an optimum adsorbent dosage

of 15 g, an optimum contact time of 150 min. and

optimum pH of 4 against an initial Cr(VI) concentration

of 292 mg/L was verified with the other physico-

chemical parameters TDS, TS, COD, BOD, and SO4

2-in

Fig. 7: Effect of contact time on removal of Cr(VI) in a tannery industry wastewater

Fig. 8: Effect of pH on removal of Cr(VI) in a tannery industry wastewater

Hexava len t chromium remo val

PercentageRemoval

Contact Time (min)

0. 0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0

0. 0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

PercentageRemoval

pH

0.0 1.0 2.0 3.0 4. 0 5.0 6.0 7.0 8.0 9. 0 10.00. 0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

PercentageRemoval


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a tannery industry wastewater. The results of maximum

reduction of various parameters TDS, TS, COD, BOD,

and SO4

2-along with reduction of Cr(VI) in a tannery

industry wastewater are presented in Table 3. The other

values of adsorbent dosage, contact time and pH werenot presented in Table 3.

From Table 3, it may be noted that the maximum

removal of various parameters TDS, TS, COD, BOD,

and SO4

2- in a tannery industry wastewater was

obtained at the same an optimum adsorbent dosage of

15 g, an optimum contact time of 150 min. and optimum

pH of 4 observed for Cr(VI) removal in a tannery

industry wastewater. Thus, the validation results (Fig.

5 and Table 3) indicated that the optimum values found

from this study were reproducing capability for

analyzing various parameters in an aqueous solution

and in any type of industrial wastewaters. Swathi et

al., (2014) found that COD reduction of 68 %, sulphatereduction of 67 %, BOD reduction of 73% and iron

reduction of 81% in a tannery industry wastewater

using rice husk as an adsorbent. The reduction of

COD, BOD, and SO4

2-in a tannery industry wastewater

using rice husk ash is found to be 81.5 %, 86.7 % and

93.4 % respectively (Table 3). The results of the present

study show a maximum reduction (Table 3) than the

previous study (Swathi et al., 2014).

Table 3: The maximum removal percentage of Cr(VI) and other physico-chemical

parameters in a tannery industry wastewater by rice husk silica powder with an

optimum adsorbent dosage of 15 g, an optimum contact time of 150 min. and

optimum pH of 4

Fig. 9: The Maximum Removal Percentage of Cr(VI) in a tannery industry wastewater and Cr(VI) in an

aqueous solution usingrice husk silica powder with an optimum adsorbent dosage of 15 g, an

optimum contact time of 150 min. and optimum pH of 4 against an initial Cr(VI) concentration

of 292 mg/L

8 8 . 3

9 3 . 5

0 . 0

1 0 . 0

2 0 . 0

3 0 . 0

4 0 . 0

5 0 . 0

6 0 . 0

7 0 . 0

8 0 . 0

9 0 . 0

1 0 0 . 0

PercentageRemoval

Tannery Industry Wastewater Aqueous Solution

Aqueous Solution

Parameters

Cr(VI)

TDS

TS

COD

BOD

SO4

2-

Initial

292 mg/L

12350 mg/L

16625 mg/L

8256 mg/L

5689 mg/L

852 mg/L

Final

34 mg/L

1074mg/L

1031mg/L

1362mg/L

757mg/L

56mg/L

Percentage Removal

88.3

91.3

93.8

81.5

86.7

93.4


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36

Isotherm Study

Adsorption isotherms are describing the distribution

of the adsorbate species among liquid phase and

adsorbed phase, based on heterogeneity or

homogeneity nature of adsorbents, type of coverageand an interaction between the adsorbate species.

Adsorption data are usually described by adsorption

isotherms, such as Langmuir and Freundlich isotherms.

These isotherms relate metal uptake per unit mass of

adsorbent, qe, to the equilibrium adsorbate

concentration in the bulk fluid phase Ce.

The Langmuir model is based on the assumption

that the maximum adsorption occurs when a saturated

monolayer of solute molecules is present on the

adsorbent surface, the energy of adsorption is

constant and there is no migration of adsorbate

molecules in the surface plane (Bhattacharya et al.,2006). The Linear form of Langmuir isotherm is written

as;

The Eqn. 3, may be rewritten as

where, Ce, q

e, q

mand b are representing the

equilibrium concentration of Cr(VI), adsorption

capacity of rice husk silica at equilibrium, maximum

adsorption capacity of rice husk silica and energy

constant related to the heat of adsorption (Langmuir

constant) respectively. The qm

and b in the Langmuir

isotherm can be determined by plotting (Ce/q

e)

versus (Ce).

It can be seen from Fig. 10 that the equilibrium data

fits the Langmuir equation well for Cr(VI) removal in atannery industry wastewater. From Fig. 6, the values

of the qm

and b were found to be 78.125 mg/g and

0.0634 L/mg for the parameter Cr(VI) in a tannery

industry wastewater. The separation factor or

equilibrium parameter RLis the essential characteristics

(Bhattacharya et al., 2006), which is dimensionless

constant, represented as;

In which, Co is the highest initial concentration of

Cr(VI) (mg/L) and b (L/mg) is Langmuir constant. The

RLvalue indicates the shape of the isotherm to beeither unfavorable (RL> 1), linear (R

L= 1), favorable (0

< RL< 1), or irreversible (R

L= 0). From Fig. 6, it was

found that the RLvalue is 0.05125, the results present

study was found to be favorable for adsorption by

rice husk silica powder for the removal of Cr(VI) in a

tannery industry wastewater.

The Freundlich isotherm model is describing the

adsorption of solutes from an aqueous phase to a solid

surface. The Freundlich isotherm assumes several

adsorption energies are involved (Bhattacharya et al.,

2006) in the adsorption process. Freundlich adsorption

isotherm is the relationship between the amounts

adsorbed per unit mass of adsorbent, q e, and the

Ce

qe=

1

qmb+

Ce

qm(3)

1

qe=

1

qmbCe+

1

qm(4)

Fig. 10: Langmuir adsorption isotherm for removal of Cr(VI) in a tannery industry wastewater

RL=1

(1+bC o)(5)

D. Sivakumar

1/Ce

1/qe

0.025

0.020

0.015

0.010

0.005

0.000

0.030

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

y = 0.2019x + 0.0128

R2= 0.9929


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37

concentration of Cr(VI) at an equilibrium, Ce. The linear

form of logarithmic equation for Freundlich isotherm is

written as;

where, Kfand n are the Freundlich constants, Kfand n are the indicators of the adsorption capacity and

adsorption intensity respectively. In this case, the plot

of log(Ce) vs log(q

e)was employed to generate the

intercept value of Kfand the slope of n.

The value of n indicates how the adsorption process

is favourable for the removal of Cr(VI) in a tannery

industry wastewater. The value of n > 1 represents the

favourable adsorption condition. From Fig. 11, it may

be noted that the equilibrium data obtained for the

Cr(VI) removal in a tannery industry wastewater fitted

with Freundlich isotherm. The values of Kfand n were

found to be 3.8963 and 4.4603 respectively, for theremoval of Cr(VI) in a tannery industry wastewater.

In order to measure the degree of relationship

between two or more variables, the correlationand

regression analysis were performed for all parameters

(Sivakumar, 2012).From Fig. 11, it may be found that n

value is greater than 1, indicates favourable adsorption

process by rice husk silica powder. From Figs. 10 and

11, it may be observed that the correlation coefficient

R2found to be 0.9929 and 0.9615 respectively for the

Langmuir and Freundlich isotherms. The results of R2

indicated that the equilibrium data of Cr(VI) removal in

a tannery industry wastewater by rice husk silica fitted

well with the Langmuir isotherm than Freundlich

isotherm. The same observations were made by Khadka

and Mishra, (2014).The previous studies also indicated

the same results as that of the present study. Apeksha

and Mote, (2014) also obtained the R2value around

0.99 for Langmuir isotherm than Freundlich isotherm(0.98). Similarly, Singhaet al., (2011) also achieved the

R2value of 0.9869 for the Langmuir isotherm.

The maximum removal of Cr(VI) was achieved at the

pH of 1.5 using rice husk (Singha et al., 2011). The

maximum removal of Cr(VI) from an aqueous solution

using rice husk ash occurred at a pH of 3 (Bhattacharya

et al., 2006) and 4 (Anand et al., 2014). Whereas, this

study removed the maximum Cr(VI) at the pH of 4 using

rice husk silica powder in a tannery industry wastewater.

The maximum removal of Cr(VI)from an aqueous

solution by rice husk ash was found to be 25.64 mg/g

(Bhattacharya et al., 2006). Nearly 45.6 mg/g removalwas achieved by Srinivasan et al., (1988), when rice

husk carbon was used for the removal Cr(VI) in an

aqueous solution, but Singh and Singh, (2012) 38.8

mg/g removal of Cr(VI) from an aqueous solution using

rice husk carbon. Apeksha and Mote, (2014) obtained

16.94 mg/g removal of Cr(VI) in an aqueous solution

using rice husk and 11.11 mg/g of Cr(VI) removal was

achieved using rice husk ash (Apeksha and Mote, 2014).

The maximum of 11.39 mg/g removal of Cr(VI) in an

aqueous solution using rice husk was achieved by

Singha et al., (2011). Whereas this study removed the

maximum Cr(VI) of 78.125 mg/g using rice husk silica

powder in a tannery industry wastewater.

Fig. 11: Freundlich adsorption isotherm for removal of Cr(VI) in a tannery industry wastewater

log(Ce)

log(qe)

y = 0.2242x + 1.3601

R2= 0.9615

2. 52. 01. 51. 0

0. 0

0. 2

0. 4

0. 6

0. 8

1. 0

1. 2

1. 4

1. 6

1. 8

2. 0

n(6)log (q

e) = log (k

f) + -log (c

e)1


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38

About 90 % removal of Cr(VI) in an aqueous solution

using rice husk ash was achieved at the pH of 4 by

Anand et al., (2014). Whereas, Singh and Singh, (2012)

found that the maximum removal (94 %) of Cr(VI) using

rice husk carbon. Nearly 79.94 % removal of Cr(VI) in atannery industry wastewater was only achieved using

rice husk (Swathi et al., 2014) and this study achieved

the removal percentage of 88.3 % in a tannery industry

using rice husk silica powder.The maximum removal of

Cr(VI) in an aqueous solution achieved with the contact

time of 180 min. (Singha et al., 2011) and 100 min. (Anand,

et al., 2014). This study removed the maximum of Cr(VI)

in a tannery industry wastewater rather than the aqueous

solution with the contact time of 150 min.

The maximum removal of Cr(VI) in an aqueous

solution and in a tannery industry wastewater depends

on the surface area presented in a rice husk, rice huskcarbon, rice husk ash and rice husk silica.The

availability of surface area depends on the method of

heat treatment, chemical treatment and contact time.

Della et al., (2002) obtained RHA specific surface area

around 54 m2/g at 700 C for 6 h and after wet grinding

for 80 min, the particles specific area increased to 81

m2/g from 54 m2/g. In this study, the specific area of

gray colour RHA (500C for 4 h) is about 242 m 2/g,

whereas specific areas of white colour RHS (650C for

6 h) are about 128 m2/g. This decrease in the specific

area is proportional to heating temperature and time;

as a result, there is an agglomeration effect and

diminishing porosity on rice husk ash (Della et al., 2002).

Further, increased specific area from 128 m2/g to 186

m2/g for RHS was obtained, when RHS was milled with

milling machine for about 60 min. for this present

study.The surface area found in the rice husk ash is

about 57.5 m2/g (Bhattacharya et al., 2006)and 105.42

m2/g (Singh and Singh, 2012). Singha et al., (2011),

found that the surface area for rice husk is about 0.54

m2/g. The increased surface area is due to increase in

porosity, which was obtained through pre-thermal

treatment. Pretreatment of rice husks can remove lignin,

hemicellulose, and reduce cellulose crystallinity

(Kumar et al., 2013).The variation of removal of Cr(VI) in an aqueous

solution and in a tannery industry wastewater of this

present study and in previous studies is due to type of

aqueous solution, the type of adsorbent, availability

of surface area, thermal treatment, chemical treatment,

contact time, initial concentration, pH and adsorbent

dosage. The important point is to be noted that all

previous studies were removed the Cr(VI) in an

aqueous solutions (Srinivasan et al., 1988; Della et al.,

2002; Bhattacharya et al., 2006; Singha et al., 2011;

Singh and Singh, 2012; Anand et al., 2014; Apeksha

and Mote, 2014), whereas Swathi et al., (2014) removedthe Cr(VI) from a tannery industry wastewater. This

study differs from the Swathi et al., (2014), because

this study removed the Cr(VI) in a tannery industry

wastewater using rice husk silica powder, but Swathi

et al., (2014) used rice husk for the removal of Cr(VI) in

a tannery industry wastewater.

CONCLUSION

In the present study, experiments have been

conducted for the removal of Cr(VI) in tannery industrial

wastewater using rice husk silica powder as an

adsorbent. To know the ability of rice husk silicapowderfor removing Cr(VI) in the tannery industrial

wastewater, the experiments were conducted with

varying adsorbent dosage, contact time and pH against

the initial concentration of 292 mg/L. The results

showed that the maximum percentage removal of Cr(VI)

in the tannery industrial wastewater at an optimum

adsorbent dosage of 15 g, contact time of 150 min., pH

of 4 respectively,using rice husk silica powder was 88.3

%. The experimental data on removal of Cr(VI) from

tannery industry wastewater is validated with the Cr(VI)

in an aqueous solution of same initial concentration of

tannery industry waster. Also, the obtained maximum

removal percentage of Cr(VI) in a tannery industry

wastewater using rice husk silica powder with an

optimum process parameters was verified with the other

physico-chemical parameters TDS, TS, COD, BOD, and

SO4

2-in a tannery industry wastewater. The Langmuir

and Freundlich adsorption isotherms were used to

check the favourable nature of the adsorption process,

but, Langmuir isotherm was found to be in good

agreement with experimental data.This study concluded

that the experimental investigation done for this study

may be reproduced for removing Cr(VI) from tannery

wastewater or from any chromium based water and

industrial wastewater.

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40

AUTHOR (S) BIOSKETCHES

Sivakumar, D.,Ph.D. is a professor in the Department of Civil Engineering, Vel Tech High Tech Dr.Rangarajan Dr.Sakunthala Engineering

College, Avadi, Chennai, Tamil Nadu, India. E-mail: [email protected]

How to cite this article: (Harvard style)

Sivakumar, D., (2015). Hexavalent chromium removal in a tannery industry wastewater using rice husk silica, Global J. Environ. Sci.

Manage. , 1 (1): 27-40.

D. Sivakumar
mailto:[email protected]:[email protected]

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Hexavalent chromium removal in a tannery industry wastewater using rice husk silica